The present invention relates to improved apparatus for generating a preset number of pulses for each revolution of a shaft, or similar device, and, more particularly, to apparatus for sensing spaced devices around the periphery of a revolving disc by the use of light beams.
The conversion of the revolutions of a shaft into analagous electric pulses is well known. Specific apparatus for such conversion is taught in U.S. Pat. No. 3,814,934 to Mesh et al, with common assignee with the present invention. In the Mesh et al patent, a pair of light sources is aligned with a pair of photocells on opposite sides of a disc mounted on the shaft. Slots radially arranged around the periphery of the disc sequentially set and reset a flip-flop as each slot allows the light from the sources to activate the photocells.
In the apparatus of the Mesh et al patent, the light sources and the photocells are positioned adjacent the revolving disc. When the revolving shaft and disc are utilized, for example, in the metering of gasoline dispensed from a pump, the disclosed apparatus entailed the positioning of electrical devices, such as light bulbs, or other sources of radiant energy and photocells within the housing of the gasoline pump.
Due to the stringent requirements for intrinsic safety controlling gasoline pumps, it was cumbersome and costly to provide barriers, screening the electrical devices from potentially explosive gaseous combinations of gasoline and air.